Liquid crystal alignment agent

ABSTRACT

A liquid crystal alignment agent containing at least two kinds of polymers selected from the group consisting of polyamic acids and imidized polymers and having a structure obtained by dehydration and ring closure of polyamic acid. In the at least two kinds of polymers contained in the liquid crystal alignment agent, the polymer of higher imidization degree has a smaller surface free energy. The liquid crystal alignment agent gives a liquid crystal display device having less stuck image and high pretilt angle.

This application claims the benefit under 35 USC 371 of prior PCTInternational Application No. PCT/JP 97/01635 which has an internationalfiling date of May 15, 1997.

TECHNICAL FIELD

The present invention relates to a liquid crystal alignment agent. Morespecifically, the present invention relates to a liquid crystalalignment agent which can give a liquid crystal alignment film havinggood liquid crystal alignability and can provide a liquid crystaldisplay device with a high pretilt angle and excellent stuck image-freeproperties.

BACKGROUND ART

There have heretofore been known TN type liquid crystal display deviceshaving a TN (twisted nematic) type liquid crystal cell which comprisestwo substrates each having, on the surface, a liquid crystal alignmentfilm via a transparent electroconductive film and a nematic liquidcrystal layer having a positive dielectric anisotropy, the nematicliquid crystal layer being interposed between the two substrates so asto form a sandwich structure, in which liquid crystal cell the majoraxes of liquid crystal molecules are continuously twisted by 90° in thedirection extending from one of the substrates to the other substrate.The alignment of liquid crystal in the TN type liquid crystal devices ismade generally by a liquid crystal alignment film imparted with analignability for liquid crystal molecules by a rubbing treatment. As thematerial for the liquid crystal alignment film, there are hitherto knownresins such as polyimide, polyamide, polyester and the like. Polyimides,in particular, are used in many liquid crystal display devices becauseof the excellency in heat resistance, compatibility with liquid crystal,mechanical strengths, etc.

When a TN type liquid crystal display device is produced using a liquidcrystal alignment film formed of conventionally used polyimide or thelike, however, the liquid crystal display device has problems in that itgives defective display due to its low pretilt angle or an imagesticking is caused owing to its a large residual voltage. Hence, it hasbeen desired to develop a liquid crystal alignment agent capable ofgiving a liquid crystal display device which has a liquid crystalalignment film of good liquid crystal alignability and a high pretiltangle and is excellent in low image retention properties.

DISCLOSURE OF THE INVENTION

The present invention has been completed in view of the above situation.The first object of the present invention is to provide a liquid crystalalignment agent capable of giving a liquid crystal alignment filmsuperior in liquid crystal alignability.

The second object of the present invention is to provide a liquidcrystal alignment agent capable of providing a high pretilt angle.

The third object of the present invention is to provide a liquid crystalalignment agent giving a liquid crystal alignment film for a liquidcrystal display device having excellent image retention properties.

The other objects and advantages of the present invention will becomeapparent from the following description.

The above-mentioned objects and advantages of the present invention canbe achieved by a liquid crystal alignment agent containing at least twokinds of polymers selected from the group consisting of polyamic acidsand imidized polymers having a structure obtained by dehydration andring closure of polyamic acid, wherein in the at least two kinds ofpolymers contained in the liquid crystal alignment agent, the polymer ofhigher imidization degree has a smaller surface free energy.

The liquid crystal alignment agent of the invention may further containan epoxy compound as an additive. In this case, it is preferable thatthe at least two kinds of the polymers have an average imidizationdegree of 5 to 40%. The liquid crystal alignment agent containing anepoxy compound possesses an effect of giving an excellent long-termstability to the resulting liquid crystal display device.

The present invention is hereinafter described in detail.

Each polymer used in the liquid crystal alignment agent of the presentinvention can be obtained by reacting at least one tetracarboxylic aciddianhydride and at least one diamine compound both mentioned below in anorganic solvent to synthesize a polyamic acid and, as necessary,subjecting the polyamic acid to dehydration and ring closure.

[Tetracarboxylic acid dianhydride]

As the tetracarboxylic acid dianhydride used in the synthesis of theabove polyamic acid, there can be mentioned, for example, aliphatic oralicyclic tetracarboxylic acid dianhydrides such asbutanetetracarboxylic acid dianhydride,1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,2-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,3-dichloro-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,2,3,4-tetramethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,2,3,4-cyclopentanetetracarboxylic acid dianhydride,1,2,4,5-cyclohexanetetracarboxylic acid dianhydride,3,3',4,4'-dicyclohexyltetracarboxylic acid dianhydride,2,3,5-tricarboxycyclopentylacetic acid dianhydride,3,5,6-tricarboxynorbornane-2-acetic acid dianhydride,2,3,4,5-tetrahydrofurantetracarboxylic acid dianhydride, 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-5-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-5-ethyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-7-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-7-ethyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-8-ethyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-5,8-dimethyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,5-(2,5-dioxotetrahydrofural)-3-methyl-3-cyclohexene-1,2-dicarboxylicacid dianhydride, bicyclo[2,2,2]-octo-7-ene-2,3,5,6-tetracarboxylic aciddianhydride and compounds represented by the following formulas (I) to(II): ##STR1## (wherein R¹ and R³ are each a bivalent organic grouphaving an aromatic ring; R² s and R⁴ s are hydrogen atoms or alkylgroups and each of two R² s and two R⁴ s may be the same or different);and aromatic tetracarboxylic acid dianhydrides such as pyromellitic aciddianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride,3,3',4,4'-biphenylsulfonetetracarboxylic acid dianhydride,1,4,5,8-naphthalenetetracarboxylic acid dianhydride,2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 3,3',4,4'-biphenylether tetracarboxylic acid dianhydride,3,3',4,4'-dimethyldiphenylsilanetetracarboxylic acid dianhydride,3,3',4,4'-tetraphenylsilanetetracarboxylic acid dianhydride,1,2,3,4-furantetracarboxylic acid dianhydride,4,4'-bis(3,4-dicarboxyphenoxy)-diphenyl sulfide dianhydride, 4,4 '-bis(3,4 -dicarboxyphenoxy)-diphenylsulfone dianhydride,4,4'-bis(3,4-dicarboxyphenoxy)-diphenylpropane dianhydride,3,3',4,4'-perfluoroisopropylidenediphthalic acid dianhydride,3,3',4,4'-biphenyltetra-carboxylic acid dianhydride, bis(phthalicacid)phenylphosphine oxide dianhydride,p-phenylene-bis(triphenylphthalic acid) dianhydride,m-phenylene-bis(triphenylphthalic acid) dianhydride,bis(triphenylphthalic acid) -4,4'-diphenyl ether dianhydride,bis(triphenylphthalic acid)-4,4'-diphenylmethane dianhydride, ethyleneglycol-bis(anhydrotrimellitate), propyleneglycol-bis(anhydrotrimellitate),1,4-butanediol-bis(anhydrotrimellitate),1,6-hexanediol-bis(anhydrotrimellitate),1,8-octanediol-bis(anhydro-trimellitate),2,2-bis(4-hydroxyphenyl)propane-bis(anhydrotrimellitate)and the compounds represented by the following formulas (1) to (4).These compounds can be used singly or in combination of two or morekinds. ##STR2##

Of the above compounds, the following compounds are preferred from theviewpoint of achievement of good liquid crystal alignability:

Butanetetracarboxylic acid dianhydride,1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,2,3,4-cyclopentanetetracarboxylic acid dianhydride,2,3,5-tricarboxycyclopentylacetic acid dianhydride,5-(2,5-dioxotetrahydrofural)-3-methyl-3-cyclohexene-1,2-dicarboxylicacid dianhydride, 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-5,8-dimethyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]-furan-1,3-dione,bicyclo[2,2,2]-octo-7-ene-2,3,5,6-tetra-carboxylic acid dianhydride,pyromellitic acid dianhydride, 3,3',4,4'-benzophenonetetracarboxylicacid dianhydride, 3,3',4,4'-biphenylsulfonetetracarboxylic aciddianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, thecompounds represented by the following formulas (5) to (7) out of thecompounds of the formula (I), and the compounds represented by thefollowing formula (8) out of the compounds of the formula (II).Particularly preferred are 1,2,3,4-cyclobutane-tetracarboxylic aciddianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic aciddianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,pyromellitic acid dianhydride and the compounds represented by thefollowing formula (5). ##STR3## [Diamine Compound]

As the diamine compound used in the synthesis of the polyamic acid,there can be mentioned, for example,

aromatic diamines such as p-phenylenediamine, m-phenylenediamine,4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane,4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenylsulfone,3,3'-dimethyl-4,4'-diaminobiphenyl, 4,41-diaminobenzanilide,4,4'-diaminodiphenyl ether, 1,5-diaminonaphthalene,3,3-dimethyl-4,4'-diaminobiphenyl,5-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane,6-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane, 3,4'-diaminodiphenylether, 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone,4,4'-diaminobenzophenone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis[4-(4-aminophenoxy)-phenyl]hexafluoropropane,2,2-bis(4-aminophenyl)hexafluoropropane,2,2-bis[4-(4-amino-phenoxy)phenyl]sulfone,1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,1,3-bis(3-aminophenoxy)benzene,9,9-bis(4-aminophenyl)-10-hydroanthracene, 2,7-diamino-fluorene,9,9-bis(4-aminophenyl)fluorene, 4,4'-methylene-bis(2-chloroaniline),2,2',5,5'-tetrachloro-4,4'-diaminobiphenyl,2,2'-dichloro-4,4'-diamino-5,5'-dimethoxybiphenyl,3,3'-dimethoxy-4,4'-diaminobiphenyl,1,4,4'-(p-phenylene-isopropylidene)bisaniline,4,4'-(m-phenyleneisopropylidene)bisaniline,2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]-hexafluoropropane,4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl,4,4'-bis[(4-amino-2-trifluoromethyl)phenoxy]-octafluorobiphenyl and thelike;

aliphatic or alicyclic diamines such as 1,1-metaxylylenediamine,1,3-propanediamine, tetramethylenediamine, pentamethylenediamine,hexamethylenediamine, heptamethylenediamine, octamethylenediamine,nonamethylenediamine, 4,4-diaminoheptamethylenediamine,1,4-diaminocyclohexane, isophoronediamine,tetrahydrodicyclopentadienylenediamine,hexahydro-4,7-methanoindanylenedimethylenediamine,tricyclo[6.2.1.02,7]-undecylenedimethyldiamine, 4,4'-methylenebis-(cyclohexylamine) and the like;

diamines having, in the molecule, two primary amino groups and anitrogen atom(s) other than the above primary amino groups, such as2,3-diaminopyridine, 2,6-diaminopyridine, 3,4-diaminopyridine,2,4-diaminopyridine, 5,6-diamino-2,3-dicyanopyrazine,5,6-diamino-2,4-dihydroxypyrimidine,2,4-diamino-6-dimethylamino-1,3,5-triazine,1,4-bis(3-aminopropyl)piperazine,2,4-diamino-6-isopropoxy-1,3,5-triazine,2,4-diamino-6-methoxy-1,3,5-triazine,2,4-diamino-6-phenyl-1,3,5-triazine, 2,4-diamino-6-methyl-s-triazine,2,4-diamino-1,3,5-triazine, 4,6-diamino-2-vinyl-s-triazine,2,4-diamino-5-phenylthiazole, 2,6-diaminopurine,5,6-diamino-1,3-dimethyluracil, 3,5-diamino-1,2,4-triazole,6,9-diamino-2-ethoxyacridine lactate,3,8-diamino-6-phenylphenanthridine, 1,4-diaminopiperazine,3,6-diaminoacridine, bis(4-aminophenyl)phenylamine, the compoundsrepresented by the following formulas (III) to (VI), and the like;##STR4## (wherein R⁵ is a monovalent organic group having anitrogen-containing ring structure selected from the group consisting ofpyridine, pyrimidine, triazine, piperidine and piperazine; and X is abivalent organic group) ##STR5## (wherein R⁶ is a bivalent organic grouphaving a nitrogen-containing ring structure selected from the groupconsisting of pyridine, pyrimidine, triazine, piperidine and piperazine;and Xs may be the same or different and are each a bivalent organicgroup) mono-substituted phenylenediamines represented by the followingformula (V): ##STR6## (wherein R⁷ is a bivalent organic group selectedfrom the group consisting of --O--, --COO--, --OCO--, --NHCO--, --CONH--and --CO--; and R⁸ is a monovalent organic group having a group selectedfrom the group consisting of a steroid skeleton, a trifluoromethyl groupand a fluoro group, or a C₆₋₃₀ alkyl group);

diaminoorganosiloxanes represented by the following formula (VI):##STR7## (wherein R⁹ s may be the same or different and are each a C₁₋₁₂hydrocarbon group; p is an integer of 1 to 3; and q is an integer of 1to 20); and

compounds represented by the following formulas (9) to (13). Thesediamine compounds can be used singly or in combination of two or morekinds. ##STR8##

In the above formulas, y is an integer of 2 to 12 and z is an integer of1 to 5.

Of the above compounds, preferred are p-phenylenediamine,4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide,1,5-diaminonaphthalene, 2,7-diaminofluorene, 4,4'-diaminodiphenyl ether,2,2-bis[4-(4-aminophenoxy)phenyl]-propane,9,9-bis(4-aminophenyl)fluorene,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane,2,2-bis(4-aminophenyl)hexafluoropropane,4,4'-(p-phenylenediisopropylidene)bisaniline,4,4'-(m-phenylenediisopropylidene)bisaniline, 1,4-cyclohexanediamine,4,4'-methylene bis(cyclohexylamine), 1,4-bis(4-aminophenoxy)benzene,4,4'-bis(4-aminophenoxy)biphenyl, the compounds represented by the aboveformulas (9) to (13), 2,6-diaminopyridine, 3,4-diaminopyridine,2,4-diaminopyridine, 3,6-diaminoacridine, the compounds represented bythe following formula (14) out of the compounds represented by the aboveformula (III), the compounds represented by the following formula (15)out of the compounds represented by the above formula (IV), and thecompounds represented by the following formulas (16) to (21) out of thecompounds represented by the above formula (V). ##STR9## [Polyamic Acid]

The tetracarboxylic acid dianhydride and the diamine compound used inthe synthesis of the polyamic acid are used in such proportions that theacid anhydride group contained in the tetracarboxylic acid dianhydrideis preferably 0.2 to 2 equivalents, more preferably 0.3 to 1.2equivalents per 1 equivalent of the amino group contained in the diaminecompound.

The synthesis of the polyamic acid is conducted in an organic solventusually at a reaction temperature of 0 to 150° C., preferably 0 to 100°C., for 1 to 48 hours. There is no particular restriction as to the kindof the organic solvent used as long as the solvent can dissolve thereaction products produced by the reaction. As the organic solvent,there can be mentioned, for example, aprotic polar solvents such asN-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethyl-formamide,dimethyl sulfoxide, γ-butyrolactone, propylene carbonate,tetramethylurea, hexamethylphosphoryl triamide and the like; andphenolic solvents such as m-cresol, xylenol, phenol, halogenated phenoland the like. The preferable amount of the organic solvent used isusually such that the total amount of the tetracarboxylic aciddianhydride and the diamine compound accounts for 0.1 to 30% by weightof the total amount of the reaction solution.

The above organic solvent can be used in combination with a poor solventfor the polyamic acid, such as alcohol, ketone, ester, ether,halogenated hydrocarbon, hydrocarbon or the like so long as the additionof the poor solvent does not cause precipitation of the formed polyamicacid. Specific examples of such a poor solvent include methyl alcohol,ethyl alcohol, isopropyl alcohol, cyclohexanol, ethylene glycol,propylene glycol, 1,4-butanediol, triethylene glycol, acetone, methylethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, butylacetate, diethyl oxalate, diethyl malonate, diethyl ether, ethyleneglycol methyl ether, ethylene glycol ethyl ether, ethylene glycolmonophenyl ether, ethylene glycol methylphenyl ether, ethylene glycolethylphenyl ether, diethylene glycol dimethyl ether, diethylene glycoldiethyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monomethyl ether acetate, diethyleneglycol monoethyl ether acetate, ethylene glycol methyl ether acetate,ethylene glycol ethyl ether acetate, 4-hydroxy-4-methyl-2-petanone,2,4-pentane-dione, 2,5-hexanedione, ethyl 2-hydroxypropionate, ethyl2-hydroxy-2-methylpropionate, ethyl 2-hydroxy-2-methylpropionate, ethylethoxyacetate, ethyl hydroxyacetate, methyl 2-hydroxy-3-methylbutanoate,methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethyl3-ethoxypropionate, methyl 3-ethoxypropionate, methyl pyruvate, ethylpyruvate, hydroxymethyl pyruvate, methyl acetoacetate, ethylacetoacetate, methylmethoxybutanol, ethylmethoxybutanol,methylethoxybutanol, ethylethoxybutanol, tetrahydrofuran,tetrahydrofurfuryl alcohol, tetrahydro-3-furanmethanol, 1,3-dioxolane,1,3-dioxepan, 4-methyl-1,3-dioxolane, dichloromethane,1,2-dichloroethane, 1,4-dichlorobutane, trichloroethane, chlorobenzene,o-dichloroethane, hexane, heptane, octane, benzene, toluene, xylene, andthe like. These solvents can be used singly or in combination of two ormore kinds.

By the above synthesis can be obtained a reaction solution containing apolyamic acid dissolved therein. The reaction solution is poured into alarge amount of a poor solvent to obtain a precipitate, and theresulting precipitate is dried under reduced pressure, whereby apolyamic acid can be obtained. Further, this polyamic acid can bepurified by again dissolving it in an organic solvent and thenconducting a step to precipitate it with the poor solvent once orseveral times.

[Imidized Polymer]

The imidized polymer constituting the liquid crystal alignment agent ofthe present invention can be produced by subjecting the polyamic acid todehydration and ring closure. The dehydration and ring closure of thepolyamic acid is conducted by (i) a method of heating the polyamic acid,or (ii) a method of dissolving the polyamic acid in an organic solvent,adding thereto a dehydrating agent and a catalyst for dehydration andring closure and, as necessary, followed by heating.

In the method (i) of heating the polyamic acid, the reaction temperatureis usually 50 to 200° C., preferably 60 to 170° C. When the reactiontemperature is lower than 50° C., the dehydration and ring closurereaction does not proceed sufficiently. When the reaction temperature ishigher than 200° C., the imidized polymer obtained may have a decreasedmolecular weight in some case.

Meanwhile, in the method (ii) of adding a dehydrating agent and acatalyst for dehydration and ring closure to a solution of the polyamicacid, there can be used, as the dehydrating agent, for example, an acidanhydride such as acetic anhydride, propionic anhydride, trifluoroaceticanhydride or the like. The amount of the dehydrating agent used ispreferably 0.01 to 20 moles per mole of the recurring unit of thepolyamic acid. As the catalyst for dehydration and ring closure, therecan be used, for example, a tertiary amine such as pyridine, collidine,lutidine, triethylamine or the like. However, the catalyst is notrestricted thereto. The amount of the catalyst for dehydration and ringclosure is preferably 0.01 to 10 moles per mole of the dehyrating agentused. Incidentally, as the organic solvent used in the dehydration andring closure, there can be cited those specific organic solventsmentioned in the synthesis of polyamic acid. The reaction temperature ofthe dehydration and ring closure is usually 0 to 180° C., preferably 10to 150° C. By applying, to the thus-obtained reaction solution, the sameoperation as employed in the purification of the polyamic acid, theformed imidized polymer can be purified.

[Terminal-modified Polymer]

The polymer constituting the liquid crystal alignment agent of thepresent invention may be a terminal-modified polymer having controlledmolecular weight. By using a terminal-modified polymer, the coatingproperties, etc. of the liquid crystal alignment agent can be improvedwithout impairment of the effects of the present invention. Theterminal-modified polymer can be synthesized by adding an acidmonoanhydride, a monoamine compound, a monoisocyanate compound or thelike to the reaction system, in the synthesis of polyamic acid. As theacid monoanhydride, there can be mentioned, for example, maleicanhydride, phthalic anhydride, itaconic anhydride, n-decylsuccinicanhydride, n-dodecylsuccinic anhydride, n-tetradecylsuccinic anhydride,n-hexadecylsuccinic anhydride and the like. As the monoamine compound,there can be mentioned, for example, aromatic monoamines such as anilineand the like; cycloalkylmonoamines such as cyclohexylamine and the like;alkylmono-amines such as n-butylamine, n-pentylamine, n-hexylamine,n-heptylamine, n-octylamine, n-nonylamine, n-decylamine, n-undecylamine,n-dodecylamine, n-tridecylamine, n-tetradecylamine, n-pentadecylamine,n-hexadecylamine, n-heptadecylamine, n-octadecylamine, n-eicosylamineand the like; and monoaminosilanes such as3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane,2-aminopropyltrimethoxysilane, 2-aminopropyltriethoxysilane,N-ethoxycarbonyl-3-aminopropyltrimethoxy-silane,N-ethoxycarbonyl-3-aminopropyltriethoxysilane,N-benzyl-3-aminopropyltrimethoxysilane,N-benzyl-3-aminopropyltriethoxysilane,N-phenyl-3-aminopropyltrimethoxysilane,N-phenyl-3-aminopropyltriethoxysilane,N-bis(oxyethylene)-3-aminopropyltrimethoxysilane, N-bis(oxyethylene)-3-aminopropyl-triethoxysilane and the like. As the monoisocyanatecompound, there can be mentioned, for example, phenyl isocyanate,naphthyl isocyanate and the like.

[Logarithmic Viscosity of Polymer]

The polymer constituting the liquid crystal alignment agent of thepresent invention has a logarithmic viscosity (ηln) of preferably 0.05to 10 dl/g, more preferably 0.05 to 5 dl/g. Herein, the logarithmicviscosity (ηln) is determined by measuring a solution containing apolymer in a concentration of 0.5 g/100 ml for its viscosity at 30° C.using an N-methyl-2-pyrrolidone as a solvent and calculating from thefollowing formula (i).

    ηln=ln [(flowing time of solution)/(flowing time of solvent)]/(weight concentration of polymer, g/dl)                           (i)

[Imidization Degree of Polymer]

The imidization degree of each polymer used in the liquid crystalalignment agent of the invention can be arbitrarily adjusted bycontrolling the catalyst amount, reaction time and reaction temperatureemployed in production of the polymer. In the present description,"imidization degree" of polymer refers to a proportion (expressed in %)of the number of recurring units of polymer forming an imide ring or anisoimide ring to the number of total recurring units of polymer. In thepresent description, the imidization degree of a polyamic acid notsubjected to dehydration and ring closure is 0%. The imidization degreeof each polymer is determined by dissolving the polymer in deuterateddimethyl sulfoxide, subjecting the resulting solution to ¹ H-NMRmeasurement at a room temperature using tetramethylsilane as a standardsubstance, and calculating from the following formula (ii).

    Imidization degree (%)=(1-A.sup.1 /A.sup.2 ×α)×100(ii)

A¹ : Peak area based on protons of NH groups (in the vicinity of 10 ppm)

A² : Peak area based on other protons

α: Proportion of the number of other protons to one proton of NH groupin polymer precursor (polyamic acid)

[Liquid Crystal Alignment Agent]

The liquid crystal alignment agent of the present invention isconstituted by at least two kinds of polymers dissolved in an organicsolvent.

The at least two kinds of polymers in the liquid crystal alignment agentof the invention have a characteristic feature in that the polymer ofhigher imidization degree has a smaller surface free energy. In the atleast two polymers constituting the liquid crystal alignment agent ofthe invention, the difference in imidization degree between the polymerof highest imidization degree and the polymer of lowest imidizationdegree is preferably 5% or more, particularly preferably 10% or more.Further, the liquid crystal alignment film obtained from the liquidcrystal alignment agent of the invention has a surface free energy ofpreferably 40 to 60 dyn/cm.

The content of the polymers in the liquid crystal alignment agent of theinvention is determined taking consideration of the viscosity,volatility and the like of the alignment agent, but is preferably 0.1 to20% by weight, more preferably 1 to 10% by weight based on the totalweight of the liquid crystal alignment agent. That is, the liquidcrystal alignment agent consisting of a polymer solution is coated onthe surface of a substrate by a printing method, spin coating method orthe like and then dried, whereby a coating film which is a material foralignment film is formed. When the content of polymers is lower than0.1% by weight, the alignment agent gives a film of too small thickness,making it impossible in some cases to obtain a good liquid crystalalignment film. When the content of polymers is higher than 20% byweight, the alignment agent gives a film of too large thickness, makingit impossible to obtain a good liquid crystal alignment film; moreover,the alignment agent has an increased viscosity and in consequence, hasinferior coating properties in some cases.

There is no particular restriction as to the organic solvent used fordissolving polymers, as long as the solvent can dissolve the polymers.As the organic solvent, there can be mentioned, for example, thosespecific organic solvents mentioned in the synthesis reaction ofpolyamic acid or its dehydration and ring closure reaction. There canalso be used, in appropriate combination with the above organic solvent,the poor solvents mentioned for combination use with an organic solventin the synthesis reaction of polyamic acid.

[Epoxy Compound]

The liquid crystal alignment agent of the present invention preferablycontains an epoxy compound as an additive. The epoxy compound ispreferably a nitrogen-containing epoxy compound. As specific examples ofthe nitrogen-containing epoxy compound, there can be mentioned:

nitrogen-containing epoxy compounds each based on an aromatic monoamine,such as N,N-diglycidylaniline, N, N-diglycidyltoluidine and the like;

nitrogen-containing epoxy compounds each based on an alicyclicmonoamine, such as N,N-diglycidylcyclohexylamine,N,N-diglycidylmethylcyclohexylamine and the like;

nitrogen-containing epoxy compounds each based on an aromatic diamine,such as N,N,N',N'-tetraglycidyl-p-phenylenediamine,N,N,N',N'-tetraglycidyl-m-phenylenediamine,N,N,N',N'-tetraglycidyl-o-phenylenediamine,N,N,N',N'-tetra-glycidyl-4,4'-diamiinodiphenylmethane,N,N,N',N'-tetraglycidyl-3,4'-diaminodiphenylmethane,N,N,N',N'-tetraglycidyl-3,3'-diaminodiphenylmethane,N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl sulfide,N,N,N',N'-tetraglycidyl-1,5-diaminonaphthalene, N,N,N'-tetraglycidyl-2,7-diaminofluorene, N,N,N'1,N'-tetraglycidyl-4,4'-diaminodiphenyl ether,N,N,N',N'-tetraglycidyl-2,2-bis[4-(4-aminophenoxy)phenyl]propane, N,N,N',N'-tetraglycidyl-9,9-bis(4-aminophenyl)fluorene,N,N,N',N'-tetraglycidyl-2,2-bis[4-(4-aminophenoxy)phenyl]-hexafluoropropane,N,N,N',N'-tetraglycidyl-2,2-bis(4-aminophenyl)hexafluoropropane,N,N,N',N'-tetraglycidyl-4,4'-(p-phenylenediisopropylidene)bisaniline,N,N,N¹,N'-tetraglycidyl-4,4'-(m-phenylenediisopropylidene)bisaniline,N,N,N',N'-tetraglycidyl-1,4-bis(4-aminophenoxy)benzene,N,N,N',N'-tetraglycidyl-4,4'-bis(4-aminophenoxy)biphenyl and the like;

nitrogen-containing epoxy compounds each based on an alicyclic diamine,such as N,N,N',N'-tetraglycidyl-m-xylylenediamine,N,N,N',N'-tetraglycidyl-p-xylylenediamine,1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane,1,4-bis(N,N'-diglycidylaminomethyl)cyclohexane,N,N,N',N'-tetraglycidyl-1,4-cyclohexanediamine,N,N,N',N'-tetraglycidyl-1,3-cyclohexanediamine,N,N,N',N'-tetraglycidyl-4,4'-methylenebis(cyclohexylamine) and the like;and

nitrogen-containing epoxy compounds each based on an aliphatic diamine,such as N,N,N',N'-tetraglycidyl-diaminoethane,N,N,N',N'-tetraglycidyl-diaminopropane,N,N,N',N'-tetraglycidyl-diaminobutane,N,N,N',N'-tetraglycidyl-diaminopentane,N,N,N',N'-tetraglycidyl-diaminohexane,N,N,N',N'-tetraglycidyl-diaminoheptane,N,N,N',N'-tetraglycidyl-diaminooctane and the like.

Of these, preferred are nitrogen-containing epoxy compounds each basedon an aromatic monoamine, nitrogen-containing epoxy compounds each basedon an aromatic diamine, and nitrogen-containing epoxy compounds eachbased on an alicyclic diamine. Particularly preferred areN,N-diglycidylaniline,N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane and1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane.

As other epoxy group-containing compounds containing no nitrogen atom,there can be mentioned, for example, ethylene glycol diglycidyl ether,polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether,tripropylene glycol diglycidyl ether, polypropylene glycol diglycidylether, trimethylolpropane triglycidyl ether, neopentyl glycol diglycidylether, 1,6-hexanediol diglycidyl ether, glycerine diglycidyl ether,2,2-dibromoneopentyl glycol diglycidyl ether and1,3,5,6-tetraglycidyl-2,4-hexanediol.

The amount of the epoxy compound is 50 parts by weight or less,preferably 0.1 to 40 parts by weight, more preferably 1 to 30 parts byweight, per 100 parts by weight of the polymers in the liquid crystalalignment agent. When the amount of the epoxy compound exceeds 50 partsby weight, the resulting liquid crystal alignment agent may have poorstorage stability.

When the epoxy compound is added to the liquid crystal alignment agentof the invention, the average imidization degree of the entire polymerin the alignment agent is preferably 5 to 40%, particularly preferably 5to 35%, further preferably 5 to 30%. A liquid crystal alignment agentcontaining polymers of an average imidization degree of above range andan epoxy compound gives a liquid crystal display device of excellentlong-term stability.

[Other Additive]

The liquid crystal alignment agent of the present invention may containa functional silane-containing compound with the view to improve theadhesivity of a polymer to the substrate surface on which the polymer iscoated. As the functional silane-containing compound, there can bementioned, for example, monoaminosilanes usable in the synthesis of theabove-mentioned terminal-modified polymer;N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,3-ureidopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane,N-triethoxysilylpropyltriethylenetriamine,N-trimethoxysilyl-propyltriethylenetriamine,10-trimethoxysilyl-1,4,7-triaza-decane,10-triethoxysilyl-1,4-7-triazadecane, 9-trimethoxy-silyl-3,6-diazanonylacetate and 9-triethoxysilyl-3,6-diazanonyl acetate. The amount of thefunctional silane-containing compound used is usually 40 parts by weightor less, preferably 0.1 to 30 parts by weight per 100 parts by weight ofthe polymers.

[Liquid Crystal Display Device]

The liquid crystal display device obtained using the liquid crystalalignment agent of the present invention can be produced, for example,by the following method.

(1) The liquid crystal alignment agent of the present invention iscoated on a transparent electroconductive film side of a substrateprovided with the transparent electroconductive film subjected to apatterning, by a method such as a roll coater method, spinner coatingmethod, printing method or the like, and then, the coated side of thesubstrate is heated thereby to form a coating film. As the substrate,there can be used a transparent substrate made of, for example, a glasssuch as float glass, soda-lime glass or the like or a plastic film ofpolyethylene terephthalate, polybutylene terephthalate,polyethersulfone, polycarbonate or the like. As the transparentelectroconductive film provided on one side of the substrate, there canbe used a NESA film made of SnO₂ an ITO film made of In₂ O₃ --SnO₂, orthe like. In patterning of the transparent electroconductive film, aphoto-etching method, a masking method or the like can be used.

Prior to coating of the liquid crystal alignment agent, a functionalsilane-containing compound, titanate or the like may be coated on thesubstrate and the transparent electroconductive film in order to furtherincrease the adhesion of the film of the alignment agent to thesubstrate and the transparent electroconductive film. The temperature ofheating is 80 to 250° C., preferably 120 to 200° C. The thickness of thefilm formed is usually 0.001 to 1 μm, preferably 0.005 to 0.5 μm.

(2) The formed coating film is subjected to a rubbing treatment in whichthe film surface is rubbed with a roll wound with a cloth made of anylon or the like in a given direction, whereby the film is impartedwith an alignability for liquid crystal molecules and becomes a liquidcrystal alignment film. Besides the rubbing treatment, there can be usedfor obtaining a liquid crystal alignment film a method of applying apolarized ultraviolet light to the surface of the coated film to impartthe film with liquid crystal alignability or a method to form a liquidcrystal alignment film by a uniaxial stretching method, aLangmuir-Blodgett method or the like. In order to remove fine powders(foreign materials) generating during the rubbing treatment to obtain aclean film surface, it is desirable to wash the liquid crystal alignmentfilm formed, with isopropyl alcohol or the like. In order to obtain aliquid crystal display device having an improved view angle, it ispossible to perform a treatment comprising applying an ultraviolet lightpartially to the liquid crystal alignment film formed with the liquidcrystal alignment agent of the invention to change the pretilt angle (asdisclosed in, for example, Japanese Laid-Open Patent Publication No.6-222366 or Japanese Laid-Open Patent Publication No. 6-281937), or atreatment comprising forming a resist film partially on the liquidcrystal alignment film subjected to a rubbing treatment, conducting arubbing treatment in a direction different from the direction of theprior rubbing treatment and then, removing the resist film thereby tochange the alignability of a liquid crystal alignment film (as disclosedin Japanese Laid-Open Patent Publication No. 5-107544).

(3) Two substrates each having a liquid crystal alignment film formedthereon are prepared as described above. They are allowed to face eachother via a gap (cell gap) in such a way that the rubbing directions ofthe two alignment films become perpendicular to each other or parallelin an opposite direction to each other. Then, the peripheries of the twosubstrates are stuck to each other using a sealing agent. A liquidcrystal is filled into the cell gap defined by the substrates and thesealing agent, and the filling hole is sealed. Thus, a liquid crystalcell is formed. Onto the outer surfaces of the liquid crystal cell, i.e.the other side of each substrate constituting the liquid crystal cell isadhered a polarizing film in such a way that the polarization directionof each polarizing film is identical or perpendicular to the rubbingdirection of the liquid crystal alignment film formed on one side ofeach substrate, whereby a liquid crystal display device is obtained.

As the sealing agent, there can be used, for example, an epoxy resincontaining a curing agent and spherical aluminum oxide as spacer.

The liquid crystal is preferably a nematic liquid crystal or a smecticliquid crystal with the former nematic liquid crystal being preferred.There is used, for example, a Schiff's base liquid crystal, an azoxyliquid crystal, a biphenyl liquid crystal, a phenylcyclohexane liquidcrystal, an ester liquid crystal, a terphenyl liquid crystal, abiphenylcyclohexane liquid crystal, a pyrimidine liquid crystal, adioxane liquid crystal, a bicyclooctane liquid crystal or a cubaneliquid crystal. It is possible to add, to such a liquid crystal, acholesteric liquid crystal such as cholesteryl chloride, cholesterylnonanate or cholesteryl carbonate, a chiral agent [e.g. C-15 or CB-15(trade name), a product of Merck Ltd.] or the like. There can also beused a ferroelectric liquid crystal such asp-decyloxybenzylidene-p-amino-2-methylbutyl cinnamate or the like.

As the polarizing plate used on the outer surface of the liquid crystalcell, there can be mentioned, for example, a polarizing plate obtainedby, while stretching a polyvinyl alcohol for orientation, allowing afilm to absorb iodine to form a polarizing film (called a H film) andinterposing the film between protective films formed of celluloseacetate, and a polarizing plate which is the H film itself.

EXAMPLES

The present invention is hereinafter described more specifically by wayof Examples. However, the present invention is not restricted to theseExamples.

First, there are mentioned the methods of evaluations for the liquidcrystal display devices produced in the following Examples andComparative Examples.

[Surface Free Energies of Polymer and Liquid Crystal Alignment Film]

Each polymer was dissolved in N-methyl-2-pyrrolidone. The resultingsolution was coated on a silicon wafer by a spin coating. The coatedwafer was heated at 100° C. for 3 hours to form a thin film. Then, thepolymer and liquid crystal alignment film were determined for surfacefree energy from the contact angle of pure water and the contact angleof methylene iodide on the above-obtained thin film and the liquidcrystal alignment film obtained in each Example, in accordance with themethod of D. K. Owens et al. described in "JOURNAL OF APPLIED POLYMERSCIENCE VOL. 13, PP. 1741-1747 (1969)", as follows.

In a system where a liquid is in contact with the surface of a solid,the relation between the surface free energy (also called as surfacetension) of the liquid, the surface free energy of the solid and thecontact angle is shown by the following formula (iii).

    (1+cosθ)×γ.sub.L =2(γ.sub.s.sup.d ×γ.sub.L.sup.d).sup.1/2 +2(γ.sub.s.sup.p ×γ.sub.L.sup.p).sup.1/2                       (iii)

γ_(L) : a surface free energy of the liquid

γ_(L) ^(d) : a dispersion term of the surface free energy of the liquid

γ_(L) ^(p) : a polarity term of the surface free energy of the liquid

γ_(s) ^(d) : a dispersion term of the surface free energy of the solid

γ_(s) ^(p) : a polarity term of the surface free energy of the solid

θ: Contact angle

Under the condition of 20°C., pure water has γ_(L) =72.8, γ_(L) ^(d)=21.8 and γ_(L) ^(p) =51.0 (units are dyn/cm in all cases); andmethylene iodide, γ_(L) =50.8, γ_(L) ^(d) =49.5 and γ_(L) ^(p) =1.3.

When these values are substituted into the above formula (iii), thefollowing formula (iv) is obtained for pure water, and the followingformula (v) is obtained for methylene iodide. Here, θ₁ and θ₂ are thecontact angle of pure water and the contact angle of methylene iodide,respectively.

    (1+cosθ.sub.1)×72.8=2(γ.sub.s.sup.d ×21.8).sup.1/2 +2(γ.sub.s.sup.p ×51.0) .sup.1/2              (iv)

    (1+cosθ.sub.2)×50.8=2(γ.sub.s.sup.d ×49.5).sup.1/2 +2(γ.sub.s.sup.p ×1.3) .sup.1/2               (v)

Hence, the measurement values of contact angles were substituted intothe formulas (iv) and (v); γ_(s) ^(d) and γ_(s) ^(p) were calculatedfrom the resulting simultaneous equations; and the surface free energyof each film was determined from the following formula (vi).

    γ.sub.s =γ.sub.s.sup.d +γ.sub.s.sup.p    (vi)

Incidentally, each contact angle was obtained using a contact anglemeasurement apparatus, Model CA-A (a product of Kyowa Kaimen KagakuK.K.), by dropping 4 μl of water or methylene iodide on a film and, oneminute thereafter, measuring the contact angle.

[Alignability of Liquid Crystal]

The presence or absence of abnormal domain in the liquid crystal cell atthe time when the voltage was On or Off was examined using a polarizingmicroscope. When there was no abnormal domain, alignment of liquidcrystal was rated as "good".

[Pretilt Angle of Liquid Crystal Display Device]

A liquid crystal display device was measured for pretilt angle by acrystal rotation method using a He-Ne laser beam, in accordance with themethod described in "T. J. Schffer et al., J. Appl. Phys., 19, 2013(1980)".

[Residual Voltage of Liquid Crystal Display Device]

A DC voltage (5 V) was applied to a liquid crystal display device at atemperature condition of 80° C. for 2 hours and then, the voltageapplication was stopped. Thereafter, the maximum voltage remaining inthe liquid crystal display device was measured.

[Reliability Test of Liquid Crystal Display Device (Presence or Absenceof Display Defect]

A liquid crystal display device was driven with a rectangular wave of 5V and 60 Hz, in a high-temperature high-humidity environment(temperature: 70° C., relative humidity: 80%). After a lapse of 1,500hours, the presence or absence of white stain-like display defect wasobserved through a polarizing microscope.

Synthesis Example 1

Into 2,000 g of N-methyl-2-pyrrolidone were dissolved 224.17 g (1.00mole) of 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 102.73 g(0.95 mole) of p-phenylenediamine and 26.04 g (0.05 mole) of cholesteryl3,5-diaminobenzoate. The resulting solution was allowed to react at 50°C. for 6 hours. The resulting reaction solution was poured into a largeexcess of pure water to precipitate a reaction product. Thereafter, thesolid was separated, washed with pure water, and dried at 40° C. underreduced pressure for 15 hours to obtain 335.3 g of a polymer (A-1)having a logarithmic viscosity (ηln) of 1.31 dl/g, an imidization degreeof 0% and a surface free energy of 52.2 dyn/cm.

Synthesis Example 2

30.0 Grams of the polymer (A-1) obtained in Synthetic Example 1 wasdissolved in 570 g of γ-butyrolactone. Thereto were added 33.3 g ofpyridine and 25.8 g of acetic anhydride, and the dehydration and ringclosure of the resulting solution was conducted at 110° C. for 3 hours.Then, the precipitation, separation, washing and drying of the reactionproduct were carried out in the same manner as in Synthesis Example 1 toobtain 28.0 g of a polymer (A-2) having a logarithmic viscosity (ηln) of1.33 dl/g, an imidization degree of 95% and a surface free energy of44.6 dyn/cm.

Synthesis Example 3

27.8 Grams of a polymer (A-3) having a logarithmic viscosity (ηln) of1.13 dl/g, an imidization degree of 80% and a surface free energy of45.9 dyn/cm was obtained in the same manner as in Synthesis Example 2except that the amounts of pyridine and acetic anhydride were changed to13.3 g and 17.2 g, respectively.

Synthesis Example 4

27.5 Grams of a polymer (A-4) having a logarithmic viscosity (ηln) of0.86 dl/g, an imidization degree of 45% and a surface free energy of48.8 dyn/cm was obtained in the same manner as in Synthesis Example 1except the amounts of pyridine and acetic anhydride were changed to 6.7g and 8.6 g, respectively.

Synthetic Example 5

330.6 Grams of a polymer (B-1) having a logarithmic viscosity (ηln) of1.18 dl/g, an imidization degree of 0% and a surface free energy of 50.2dyn/cm was obtained in the same manner as in Synthesis Example 1 exceptthat cholesteryl 3,5-diaminobenzoate was replaced by 21.12 g (0.05 mole)of the diamine compound of the formula (20). Then, 26.9 g of a polymer(B-2) having a logarithmic viscosity (ηln) of 1.07 dl/g, an imidizationdegree of 93% and a surface free energy of 43.8 dyn/cm was obtained inthe same manner as in Synthesis Example 2 except that the polymer (A-1)was replaced by 30.0 g of the polymer (B-1). Further, 26.7 g of apolymer (B-3) having a logarithmic viscosity (ηln) of 0.89 dl/g, animidization degree of 82% and a surface free energy of 44.6 dyn/cm wasobtained in the same manner as in Synthesis Example 3 except that thepolymer (A-1) was replaced by 30.0 g of the polymer (B-1).

Synthetic Example 6

420.9 Grams of a polymer (C-1) having a logarithmic viscosity (ηln) of1.02 dl/g, an imidization degree of 0% and a surface free energy of 50.1dyn/cm was obtained in the same manner as in Synthesis Example 1 exceptthat 2,3,5-tricarboxycyclopentylacetic acid dianhydride was replaced by314.30 g (1.00 mole) of1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione.Then, 27.5 g of a polymer (C-2) having a logarithmic viscosity (ηln) of0.86 dl/g, an imidization degree of 99% and a surface free energy of42.2 dyn/cm was obtained in the same manner as in Synthesis Example 2except that the polymer (A-1) was replaced by 30.0 g of the polymer(C-1).

Synthesis Example 7

313.0 Grams of a polymer (D-1) having a logarithmic viscosity (ηln) of1.89 dl/g, an imidization degree of 0% and a surface free energy of 57.2dyn/cm was obtained in the same manner as in Synthesis Example 1 exceptthat 218.12 g (1.00 mole) of pyromellitic acid dianhydride was used asthe tetracarboxylic acid dianhydride and 108.14 g (1.00 mole) ofp-phenylenediamine was used as the diamine compound.

Synthesis Example 8

603.0 Grams of a polymer (E-1) having a logarithmic viscosity (ηln) of1.59 dl/g, an imidization degree of 0% and a surface free energy of 53.3dyn/cm was obtained in the same manner as in Synthesis Example 1 exceptthat 224.17 g (1.00 mole) of1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride wasused as the tetracarboxylic acid dianhydride and 410.52 g (1.00 mole) of2,2-bis[4-(4-aminophenoxy)phenyl]propane was used as the diaminecompound.

Synthesis Example 9

315.7 Grams of a polymer (F-1) having a logarithmic viscosity (ηln) of1.69 dl/g was obtained in the same manner as in Synthesis Example 1except that 108.14 g (1.00 mole) of p-phenylenediamine was used as thediamine compound. Then, 28.4 g of a polymer (F-2) having a logarithmicviscosity ( n ln) of 1.70 dl/g, an imidization degree of 95% and asurface free energy of 57.5 dyn/cm was obtained in the same manner as inSynthesis Example 2 except that the polymer (A-1) was replaced by 30.0 gof the polymer (F-1).

Synthesis Example 10

Into 1,300 g of N-methyl-2-pyrrolidone were dissolved 224.17 g (1.00mol) of 2,3,5-tricarboxycyclopentylacetic acid dianhydride, 97.33 g(0.90 mole) of p-phenylenediamine and 42.24 g (0.10 mole) of the diaminecompound of the formula (20). The resulting solution was allowed toreact at 40° C. for 6 hours. The resulting reaction solution was pouredinto a large excess of pure water to precipitate a reaction product. Thesolid was separated, washed with pure water, and dried at 40° C. underreduced pressure for 15 hours to obtain 334.9 g of a polymer (a-1)having a logarithmic viscosity (ηln) of 1.35 dl/g and an imidizationdegree of 0%.

30.0 Grams of the obtained polymer (a1) was dissolved in 570 g ofγ-butyrolactone. Thereto were added 33.3 g of pyridine and 25.8 g ofacetic anhydride, and the dehydration and ring closure of the resultingsolution was conducted at 110° C. for 4 hours. Then, the precipitation,separation, washing and drying of the reaction product were conducted inthe same manner as in Synthesis Example 1 to obtain 28.3 g of a polymer(a-2) having a logarithmic viscosity (ηln) of 1.36 dl/g and animidization degree of 90%.

Synthesis Example 11

416.76 Grams of a polymer (a-3) having a logarithmic viscosity (ηln) of1.32 dl/g and an imidization degree of 0% was obtained in the samemanner as in Synthesis Example 10 except that the tetracarboxylic aciddianhydride used in Synthesis Example 10 was replaced by 314.30 g (1.00mole) of1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione.Then, 28.5 g of a polymer (a-4) having a logarithmic viscosity (ηln) of1.28 dl/g and an imidization degree of 100% was obtained in the samemanner as in Synthesis Example 2 except that the polymer (A-1) wasreplaced by 30.0 g of the polymer (a-3) and that the reactiontemperature in dehydration and ring closure was changed to 80° C.

Synthesis Example 12

305.7 Grams of a polymer (a-5) having a logarithmic viscosity (ηln) of1.78 dl/g and an imidization degree of 0% was obtained in the samemanner as in Synthesis Example 1 except that the diamine compound usedin Synthesis Example 10 was changed to 108.16 g (1.00 mole) ofp-phenylenediamine.

Synthesis Example 13

299.9 Grams of a polymer (a-6) having a logarithmic viscosity (ηln) of2.01 dl/g and an imidization degree of 0% was obtained in the samemanner as in Synthesis Example 1 except that 218.12 g (1.00 mole) ofpyromellitic acid dianhydride was used as the tetracarboxylic aciddianhydride used in Synthetic Example 12 and 108.16 g (1.00 mole) ofp-phenylenediamine was used as the diamine compound used in SyntheticExample 12.

Example 1

(1) Preparation of liquid crystal alignment agent

1.0 Gram of the polymer (A-1) obtained in Synthetic Example 1 and 4.0 gof the polymer (A-2) obtained in Synthetic Example 2 were dissolved inN-methyl-2-pyrrolidone to obtain a solution having a solid content of 4%by weight. The solution was passed through a filter having a porediameter of 1 μm to prepare a liquid crystal alignment agent.

(2) Preparation of liquid crystal display device

(i) The liquid crystal alignment agent prepared above was coated on atransparent electroconductive film (comprising an ITO film) provided onone surface of a glass substrate of 1 mm in thickness, by using aprinting machine for formation of liquid crystal alignment film. Thecoated substrate was dried at 180° C. for 1 hour to form a coating film.The coating film was measured for uniformity, which gave an average filmthickness of 489 and the maximum thickness difference of 17.

(ii) The coating film surface was subjected to a rubbing treatment,using a rubbing machine having a roll wound round with a rayon cloth, toimpart it with alignability for the liquid crystal molecules, therebyproducing a liquid crystal alignment film. The rubbing conditions wereroll rotation of 500 rpm and stage transfer speed of 1 cm/sec.

(iii) Thus was produced two substrates each having a liquid crystalalignment film. The periphery of each substrate was coated, by a screenprinting, with an epoxy resin containing spherical aluminum oxide(particle diameter of 17 μm). The resulting two substrates were allowedto face each other via a gap in such a way that the rubbing directionsof the two liquid crystal alignment films became perpendicular orparallel in an opposite direction to each other. The peripheries of thetwo substrates were allowed to abut on each other and press-bonded, andthe adhesive was cured.

(iv) Into the cell gap defined by the surface of the substrates and theadhesive at the peripheries was filled a nematic liquid crystal,MLC-2001 (a product of Merck Japan Ltd). Then, a filling hole was sealedwith an epoxy type adhesive to constitute a liquid crystal cell.Thereafter, on the outer surfaces of the liquid crystal cell was adheredpolarizing films in such a way that the polarization direction of thepolarizing film became identical with the rubbing direction of liquidcrystal alignment film formed on one side of the substrate, whereby aliquid crystal display device was produced.

The liquid crystal display device was evaluated for alignment of liquidcrystal and pretilt angle. The alignment of liquid crystal was good, andthe pretilt angle was as high as 5.3 0. The residual voltage was as lowas 0.16 V. The results are shown in Table 1.

Examples 2 to 9

Using the polymers obtained in Synthesis Examples 1 to 8, in theformulation shown in Table 1, various liquid crystal alignment agents ofthe present invention were produced in the same manner as in Example 1(1). Using the thus-obtained liquid crystal alignment agents, variousliquid crystal display devices were produced in the same manner as inExample 1 (2).

Each of the liquid crystal display devices was evaluated for alignmentof liquid crystal, pretilt angle and residual voltage. The results areshown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________         Polymers                                                                              Composition                                                           Imidization                                                                           ratio of                                                                            Surface free                                                    degree (%)                                                                            polymers                                                                            energy of                                                                            Alignability                                                                        Residual                                                                           Pretilt                                       Surface free                                                                          (Weight                                                                             alignment                                                                            of liquid                                                                           voltage                                                                            angle                                    Example                                                                            energy (dyn/cm)                                                                       ratio)                                                                              film (dyn/cm)                                                                        crystal                                                                             (V)  (°)                               __________________________________________________________________________    1    A-1 A-2 20:80 45.4   Good  0.16 5.3                                           0   95                                                                        52.2                                                                              44.6                                                                 2    A-1 A-2 50:50 45.7   Good  0.18 5.0                                           0   95                                                                        52.2                                                                              44.6                                                                 3    A-1 A-2 80:20 46.2   Good  0.20 4.8                                           0   95                                                                        52.2                                                                              44.6                                                                 4    A-2 A-3 50:50 45.3   Good  0.19 5.5                                           95  80                                                                        44.6                                                                              45.9                                                                 5    A-2 A-4 20:80 45.6   Good  0.18 5.2                                           95  45                                                                        44.6                                                                              48.8                                                                 6    B-1 B-2 50:50 45.4   Good  0.20 4.5                                           0   93                                                                        50.2                                                                              43.8                                                                 7    C-1 C-2 50:50 42.8   Good  0.22 4.9                                           0   99                                                                        50.1                                                                              42.2                                                                 8    D-1 A-2 50:50 45.8   Good  0.11 4.8                                           0   95                                                                        57.2                                                                              44.6                                                                 9    E-1 A-2 50:50 46.1   Good  0.23 4.7                                           0   95                                                                        53.3                                                                              44.6                                                                 __________________________________________________________________________

Examples 10 to 15

Using the polymers obtained in Synthesis Examples 10 to 13 and epoxycompounds, in the formulation shown in Table 2, various liquid crystalalignment agents of the present invention were produced in the samemanner as in Example 1 (1). Using the thus-obtained liquid crystalalignment agents, various liquid crystal display devices were producedin the same manner as in Example 1 (2).

Each of the liquid crystal display devices was evaluated for alignmentof liquid crystal, pretilt angle and residual voltage. The results areshown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________       Polymers      Epoxy                                                           Imidization                                                                           Composition                                                                         compound                                                                           Surface free                                               degree (%)                                                                            ratio of                                                                            (b)  energy of                                                  Surface free                                                                          polymers                                                                            Weight                                                                             alignment                                                                           Alignability                                                                        Residual                                                                           Pretilt                                   energy  (Weight                                                                             ratio of                                                                           film  of liquid                                                                           voltage                                                                            angle                                                                             Reliabi-                           Ex.                                                                              (dyn/cm)                                                                              ratio)                                                                              (a):(b)                                                                            (dyn/cm)                                                                            crystal                                                                             (V)  (°)                                                                        lity                               __________________________________________________________________________    10 a-2 a-5 20:80 b-1  44.3  Good  0.03 4.7 Good                                  90  0         80:20                                                           43.0                                                                              54.4                                                                   11 a-2 a-5  6:94 b-1  44.4  Good  0.03 4.5 Good                                  90  0         80:20                                                           43.0                                                                              54.4                                                                   12 a-2 a-6 20:80 b-1  45.1  Good  0.05 5.0 Good                                  90  0         80:20                                                           43.0                                                                              58.3                                                                   13 a-4 a-6 20:80 b-1  44.9  Good  0.09 4.8 Good                                  100 0         80:20                                                           42.1                                                                              58.3                                                                   14 a-2 a-5 20:80 b-2  44.2  Good  0.08 5.1 Good                                  90  0         80:20                                                           43.0                                                                              54.4                                                                   15 a-2 a-5 20:80 b-3  44.3  Good  0.15 5.0 Good                                  90  0         80:20                                                           43.0                                                                              54.4                                                                   __________________________________________________________________________     Ex.: Example                                                             

Comparative Examples 1 to 5

Using the polymers obtained in Synthesis Examples 1 to 15, in theformulation shown in Table 3, various liquid crystal alignment agentsfor comparison were produced in the same manner as in Example 1 (1).Using the thus-obtained liquid crystal alignment agents, various liquidcrystal display devices were produced in the same manner as in Example 1(2).

Each of the liquid crystal display devices was evaluated for alignmentof liquid crystal, pretilt angle and residual voltage. The results areshown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________        Polymers      Epoxy                                                                              Surface                                                    Imidization                                                                           Composition                                                                         compound                                                                           free                                                       degree (%)                                                                            ratio of                                                                            (b)  energy of                                                  Surface free                                                                          polymers                                                                            Weight                                                                             alignment                                                                          Alignability                                                                        Residual                                                                           Pretilt                                Comp.                                                                             energy  (Weight                                                                             ratio of                                                                           film of liquid                                                                           voltage                                                                            angle                                  Ex. (dyn/cm)                                                                              ratio)                                                                              (a):(b)                                                                            (dyn/cm)                                                                           crystal                                                                             (V)  (°)                             __________________________________________________________________________    1   A-1     --    --   52.2 Bad   0.08 1.1                                        0             --                                                              52.2                                                                      2   A-2     --    --   44.6 Good  0.89 7.3                                        95            --                                                              44.6                                                                      3   A-2 B-3 50:50 --   44.6 Good  0.65 6.7                                        95  82        --                                                              44.6                                                                              44.6                                                                  4   A-1 F-2 50:50 --   56.0 Good  0.73 4.3                                        0   95        --                                                              52.2                                                                              57.5                                                                  5   a-2     --    b-1  45.0 Good  11.1 4.9                                        100           80:20                                                           43.0                                                                      __________________________________________________________________________     Comp. Ex.: Comparative Example                                           

In Table 2 and Table 3, the symbols for epoxy compounds are for thefollowing epoxy compounds.

b-1: N,N,N',N'-Tetraglycidyl-4,4'-diaminodiphenylmethane

b-2: 1,3-Bis(N,N'-diglycidylaminomethyl)cyclohexane

b-3: Trimethylolpropane triglycidyl ether

According to the present invention there is obtained a liquid crystalalignment agent capable of giving a liquid crystal display device havingless stuck image and high pretilt angle.

The liquid crystal device having a liquid crystal alignment film formedwith the liquid crystal alignment agent of the invention can befavorably used in a TN type liquid crystal display device and, byselecting the liquid crystal to be used, also in liquid crystal displaydevices of IPS (in-plane-switching) type, STN (super twisted nematic)type, SH (super homeotropic) type, ferroelectric type, antiferroelectrictype, etc.

The liquid crystal display device having a liquid crystal alignment filmformed with the liquid crystal alignment agent of the invention issuperior in alignment of liquid crystal and reliability, and can beeffectively used in various display devices such as desk calculator,wrist watch, desk clock, digital display panel, word processor, personalcomputer, liquid crystal TV and the like.

We claim:
 1. A liquid crystal alignment agent comprising a mixture ofpolyamic acids and imidized polymers wherein the imidized polymers areobtained by dehydration and ring closure of polyamic acid, and whereinthe polymer having a higher imidization degree has a smaller surfacefree energy.
 2. The liquid crystal alignment agent according to claim 1,wherein the difference in imidization degree between the polymer ofhighest imidization degree and the polymer of lowest imidization degreeis 5% or more and the surface free energy of a liquid crystal alignmentfilm obtained from the liquid crystal alignment agent is 40 to 60dyn/cm.
 3. The liquid crystal alignment agent according to claim 1,further comprising an epoxy compound and wherein the polyamic acids andthe imidized polymers contained in the liquid crystal alignment agenthave an average imidization degree of 5 to 40%.
 4. The liquid crystalalignment agent according to claim 3, wherein the epoxy compound is anitrogen-containing epoxy compound.
 5. The liquid crystal alignmentagent according to claim 1, wherein each of the polyamic acids andimidized polymers independently comprise, as a constituent, at least onetetracarboxylic acid dianhydride selected from the group consisting ofbutanetetracarboxylic acid dianhydride,1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,1,2,3,4-cyclopentanetetracarboxylic acid dianhydride,2,3,5-tricarboxycyclopentylacetic acid dianhydride,5-(2,5-dioxotetrahydrofural)-3-methyl-3-cyclohexane-1,2-dicarboxylicacid dianhydride,1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho-[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-5,8-dimethyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,bicyclo[2,2,2]-octo-7-ene-2,3,5,6-tetracarboxylic acid dianhydride,pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic aciddianhydride, 3,3',4,4'-biphenylsulfonetetracarboxylic acid dianhydride,1,4,5,8-naphthalenetetracarboxylic acid dianhydride and the compoundsrepresented by the following formulas (5) to (8): ##STR10##
 6. Theliquid crystal alignment agent according to claim 1, wherein each of thepolyamic acids and imidized polymers independently comprise, as aconstituent, at least one diamine compound selected from the groupconsisting of p-phenylene diamine, 4,4'-diaminodiphenylmethane,3,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane,4,4'-diaminodiphenyl sulfide, 1,5-diaminonaphthalene,2,7-diaminofluorene, 4,4'-diaminodiphenyl ether,2,2-bis[4-(4-aminophenoxy)phenyl]-propane,9,9-bis(4-aminophenyl)fluorene,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane,2,2-bis(4-aminophenyl)hexafluoropropane,4,4'-(p-phenytenediisopropylidene)bisaniline,4,4'-(m-phenylenediisopropylidene)bisaniline,2,2-bis[4-(4-aminophenoxy)phenyl]sulfone, 1,4-cyclohexanediamine,4,4'-methylene bis(cyclohexylamine), 1,4-bis(4-aminophenoxy)-benzene,4,4'-bis(4-aminophenoxy)biphenyl, the compounds represented by thefollowing formulas (9) to (21):
 2. 6-diaminopyridine,3,4-diaminopyridine, 2,4-diaminopyridine and 3,6-diaminoacridine.
 7. Theliquid crystal alignment agent according to claim 3, wherein each of thepolyamic acids and imidized polymers independently comprise, as aconstituent, at least one kind of tetracarboxylic acid dianhydrideselected from the group consisting of 1,2,3,4-cyclobutanetetracarboxylicacid dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic aciddianhydride, 2,3,5-tricarboxycyclopentylacetic acid dianhydride,1,3,3a,4,5,9b-hexahydro-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,1,3,3a,4,5,9b-hexahydro-8-methyl-5-(tetrahydro-2,5-dioxo-3-furanyl)-naphtho[1,2-c]furan-1,3-dione,pyromellitic acid dianhydride and the compounds represented by thefollowing formula (5): ##STR11##
 8. The liquid crystal alignment agentaccording to claim 4, wherein the nitrogen-containing epoxy compound isat least one compound selected from the group consisting ofnitrogen-containing epoxy compounds derived from an aromatic monamine,nitrogen-containing epoxy compounds derived from an aromatic diamine andnitrogen-containing epoxy compounds derived from an alicyclic diamine.9. The liquid crystal alignment agent according to claim 8, wherein thenitrogen-containing epoxy compound is at least one compound selectedfrom the group consisting of N,N-diglycidylaniline,N,N,N',N'-tetraglycidyl-4-4'-diaminodiphenylmethane and1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane.
 10. A liquid crystalalignment film, comprising the liquid crystal alignment agent as claimedin claim 1.